Method of and apparatus for preventing slagging in tubular element gas heating furnaces



Aug. 28, 1951 2,565,857

5 H. KLEIBER METHOD OF AND APPARATUS FOR PREVENTI SLA NG IN TUB ING FACE 2 Sheets-Sheet 1 ULAR ELEMENT GAS HEAT Filed May 15. 1946 Fig.1

A I lnucn'ior 19 19 Hanna Kleib er Attorneys 1951 KLEIBER 2,565,357

METHOD OF AND AP RATU OR R VENTI SLAGGING IN TUBULAR ELEMENT s 1-1 ING FAGES 7 2 Sheets-Sheet 2 Filed May 15, 1946 Inventor Heinz KleiberPatented Aug. 28, 1951 PAT ENT oF icE-- i i2;565,s57 r I METHQDomsnmmrnsiros liliE- NENI N SL GGI N IUB GAS HEATING FURNACES Heinz"Kleiber, "Zurich, Switzerland, assigndr to Aktiengesellschaft 'FuerTechnische Studien, Zurich, Switzerland, a corporation of SwitzerlandApplication May15,?1946, Serial No. 669.867 *ln switzerlahd May 28,1945

z-ciaims. ---(c1. 126-409) This invention relates to a tubular gasheater which is designed lin -particular for thermal power plants inwhich a gaseous'working medium, preferably air, is to be brought toa'higher temperature in a heater'by an indirect supply of heat from anexternal source.

In heaters of this kind'theworking medium has to be heated totemperatures between 600 and 700 C. and even more,thetempe'rature in thefurnace chamber becoming in such case correspon'dingly high. Iftherefore fuels'which slag, such as pulverizedcoal for example have tobe burnt in'the heater, there is risk that liquid particles of slagwill'remainattach'ed tothe very hot heater tubes whichishighly'undesirable, asthis can lead to heavy slagging in thefurnacechamber in a shorttiiher The heater tubes must also be protected fromthe radiant heat of the fire gases, to which end it has already beenproposed to return part of the flue gases to the furnace chamber in sucha way that they form a cooling layer between the fire gases and theheater tubes. Inthis connectionthe'object"of'the present invention is toenable further improvements tooe achieved by causing the returned fluegases to enter the furnace chamber through g'ap s between the tubes ofthe heater, at leastat those parts which are most endangered andhottest. In this way it can be ensuredthat the fluegases which enterthrough the --gaps and are already cooled down, will blow the sticky oreven liquid particles of slag away from the tubes and also cool themdown below their melting point, so that they solidify and liquid slagcannot in any case become deposited on the tubes. The application of theinvention is therefore desirable when the fuel burnt in the furnacechamber gives rise to the production of solid or liquid constituents(that is to say sand for example when blast furnace gases are burnt).The flame also will be forced away from the tubes by the returned fluegases so that no tongues of fire can come into contact with the tubes.The layer of flue gases, which, on account of the contained carbonicacid and water affords efficient protection against radiation, can neverbe churned up into eddies, overheated and torn away in the furnacechamber, by the turbulence of the flue gases, as it is continuallyrenewed from the heating surface. The new technical rule according tothis invention also enables an equalisation of the tube wall temperatureand heat supply to be brought about, as the cold parts of the tubes,that is to say the sides of them which are turned away from the flameare heated by the returned flue gases, while those parts ofthetubeswhich are too hot are cooled. Furthermore the combustion'chamber hasonly to .be isolated-from the temperature of the returned flue "gases;any'p'ossibly irradiated and heated p'artsiof the walls of this chamber,are co'ol'edby thereturnedfluega's'es. 1

Several constructional forms of the. subject matter of theinvention-are: shown by way-of example in' a simplified-form ofrepresentation the accompanying drawings? in which:

- -:'Fig. 1 shows a heater in'whichair'usedas'work-' mg medium in apower plant isto'b'e heated, said air. .flowirigfthrough-a part of the'heater heated.

by" radiation and through a part heated by contact in twoparallelcurrentsxfl I V 'Fig.-.-2-is a section onrthe line 11-11 of-'Fig. 1, the parts of the heaterwhich ar'e"situated-below this sectionbeing omitted for the sake of simplicity, the tubes b'einginotsectioned.

Fig. 3 shows in a view corresponding to'that'iof Fig. 1 a secondembodiment of the invention.

*Figef4shows'inaaf'horizontal section a part of anh'eaterinWhichthetubesare fixed in their relative position by distance piecesya'nd Fig.5ash'ows a part of a heater'in'which-gaps are provided between groups oftubes only, each of these groups consisting of two tubes and beingafi'ixed. to the, boundary fwall of :the. furnace chamber, "and thetubes being not shown in :sec-

' tion. I

In the Figures 1 and 2 numeral i denotes the furnace chamber, that is tosay the combustion chamber, of a coal dust-fired heater A of a thermalpower plant, in which air serving as working medium describes a cycleand in doing so is brought in a two-casing compressor 2, 3 to a higherpressure, then heated indirectly in the heater A by an external supplyof heat and afterwards expanded in a turbine 4 which supplies energyboth to the compressor 2, 3 and also to a consumer of useful output 5.Air for the support of combustion is mixed with the coal dust in a pipe6. This air for the support of combustion is brought to the requiredtemperature in a preheater 1, which is heated by the flue gases escaping from the heater A, and it then passes through a pipe 8 into the pipe6. The combustion chamber t is lined with tubes 9 through which a partof the air of the cycle which is to be heated flows. A part of the heatcontained in the fire gases is given up to these tubes 9 in thecombustion chamber I mainly by radiation. From the combustion chamber 1the fire gases pass into a second chamber ID, in which a heating systemI l is ar-- ranged to which the fire gases give up heat by 3 contact.The air to be heated in the heater A enters through a pipe I2 anddivides at the distributor [3 into two parallel currents, one of whichflows in the same direction as the fire gases through the. tubes 9 andtheother in the opposite direction to the fire gases through the heatingsystem H. The parallel currents thus heated combine again at thecollector M, where they enter a pipe l connected to the inlet of theturbine 4 and thus forming a further component of the cycle which theair, heated in the manner described, has to pursue. A part of the gasesescaping from the chamber 10, that is to say, a

part of what is usually termed flue gases, passes.

into a pipe IS, in which a blower I1 is arranged, so that said part ofthe flue gases is returned to the furnace chamber I. Theremainder of theflue gases passes, after flowing through the pass [8, in which the abovementioned air preheater I is arranged, out into the open air.

.The tubes 9, which line the furnace chamber I, are so arranged thatgaps I9. (Fig. 2) are left free between them. Through these gaps IS theflue gases delivered by the blower I! pass into the furnace chamber I,blowing any particles of slag present off the tubes 9 in the mannershown in Fig. 2.

As shown in Fig. 3, thegaps between the heater tubes do not need toextend over the whole length of these tubes, as it may sufiice for thereturned flue gases to pass between the tubes into the furnace chamberat those parts of the heater at least which are most endangered andhottest, i. e. only between the lower end of these tubes 20 up to thepoint B. In this second embodiment of the invention the tubes 20 arefixed in their relative positions by distance pieces 2| (Fig. 4), sothat the necessary Width of the gaps between the tubes 20 for theblowing in of returned flue gases is preserved.

As shown in Fig. 5, instead of providing a gap between every twoadjacent tubes for blowing returned flue gases into the combustionchamber, gaps may be provided between groups 23 only which consist eachof two pipes 24. Each group 23 is afiixed to the boundary wall 21 of thefurnace chamber 25 by a support 26.

The invention can be ,used with any arrangement and position of thetubes in the furnace chamber. The arrangement and direction of the 4flame in the furnace chamber likewise do not constitute essentialfeatures of the invention.

What is claimed is: 1. In a tubular gas heater, the combination of afurnace structure having walls enclosing a combustion chamber and anoiftake passage leading therefrom; a tubular heat exchanger lining thecombustion chamber and comprising a plurality oftubes spaced from oneanother and from the walls of the combustion chamber, the spacing of thetubes from the walls being greater than the spacing of the tubes fromone another and the two spacings being so chosen that the intervalbetween the lining and the chamber walls serves as a manifold space fordistributing gases to be discharged through the inter-tube spaces;connections for passing gas to be heated through said tubular exchanger;a burner communicating with the combustion chamber and arranged to causecombustion therein within the space lined by said tubular heatexchanger; and means for drawing a portion of the products of combustionfrom said ofitake passage and discharging it under pressure into saidmanifold space.

2. The method of resisting deposition of slag on the surfaces of a rowof spaced heat exchange tubes, which comprises burning a slag evolvingfuel at one side of said row of spaced tubes whereby the tubes areexposed on that side to radiant heat generated by combustion; anddelivering a hot gaseous medium at a temperature lower than thetemperature of combustion against the other side of said row of tubesunder pressure sufficient to cause said medium to flow through thevari-' ous inter-tube spaces and in a direction toward said burningfuel.

HEIN Z KLEIBER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Gygi July 10, 1945

